Cannabis-dependent patients may be at risk of post-surgery complications – study

Cannabis-dependent patients may be at an increased risk of complications following minor surgery, according to a new study.

Patients who are dependent on cannabis may face higher infection rates following knee and shoulder arthroscopy—a minimally invasive surgery in which a small camera is inserted to diagnose and sometimes treat injury.

Although the effect of cannabis use is increasingly being investigated, few studies have looked at the potential effects of cannabis in patients who are undergoing surgery. 

A team of researchers from the University of Chicago set out to determine if cannabis-dependent users face an increased risk of complications following knee or shoulder arthroscopy.  

Using PearlDiver, a national insurance claims database, researchers from the University of Chicago performed a retrospective study of patients with cannabis dependence who underwent knee or shoulder arthroscopy for the postoperative complications of deep vein thrombosis (DVT), pulmonary embolism (PE), and infection.  

How the study worked 

All patients undergoing knee or shoulder arthroscopy were identified retrospectively in PearlDiver. Patients who had a diagnostic code for cannabis dependence were also identified within each surgery category. 

The definition requires patients to meet three or more criteria, such as using cannabis longer than intended, difficulty in cutting down use, spending a lot of time in obtaining or recovering from cannabis and high tolerance.  

The rates of DVT, PE, and infection within 90 days were assessed for all patients.

Univariate analyses of cannabis dependence on all outcomes were performed, followed by a multivariate logistic regression analysis controlling for known patient comorbidities (other medical conditions). 

The key findings 

The researchers identified 1,113,944 knee and 747,938 shoulder arthroscopy patients. Out of those 1,861,892 patients, 21,823 patients had a diagnostic code for cannabis dependence.  

Within both subgroups, the cannabis dependence cohort experienced increased rates of infection and DVT, while the PE rate stayed the same.  For the shoulder arthroscopy group, the rates of infection increased from 0.7%  to 1.7%, the DVT rate from 0.2% to 0.4%, while PE stayed at 0.2%. 

In the knee arthroscopy group, the rates of infection increased from 1.1% to 2.6%, the DVT rate rose from 0.2 to 0.3%, and PE stayed at 0.3%.   

In the multivariate analyses controlling for a variety of patient risk factors, including tobacco use or a history of diabetes, cannabis dependence was identified as an independent risk factor for infection within both cohorts. 

The findings were presented at the Scientific Forum of the American College of Surgeons (ACS) Clinical Congress 2022. 

What this means for patients 

Lead study author Sarah Bhattacharjee, MD, who conducted the research while she was a medical student at the University of Chicago. 

“Marijuana has been gaining so much popularity, but it’s a risk factor we aren’t really catching. 

“The higher infection rate found by this new study should raise a ‘red flag’ for patients and providers and should be discussed along with other risk factors before an arthroscopic procedure.” 

Study co-author Jason Strelzow, MD and assistant professor of orthopaedic surgery, University of Chicago added: “There’s so much information out there on smoking, alcohol, and other substances, but not on marijuana use.

“As providers and surgeons, we should be discussing marijuana use with our patients, something that we have traditionally shied away from.” 

Dr Strelzow hopes surgeons will use the study results to help inform cannabis-dependent patients about risks, benefits, and available alternatives, such as reducing or eliminating cannabis use six months prior to an arthroscopic procedure. 

Although the study focused on minimally invasive surgery, Dr Strelzow said that ‘we would expect similar or larger effects with more open or invasive procedures’.

The study has identified the need for additional research to better understand the relationship between cannabis dependence and postoperative complications.

In addition, given that the study used very rigid criteria for cannabis dependence, there are opportunities for future clinical studies to investigate how various levels of cannabis use impact postoperative complications.

• Deepening the search for cannabis plant’s best kept secrets
• Medical cannabis patients at ‘low risk’ of hospitalisation from mental disorders – study
• What is the risk of dependence in medical cannabis patients?
• How sex, hormones and adolescence play a role in THC’s effects
• Medical students have “little knowledge” of cannabis, study finds